Although single-celled, there is nothing primitive or simple about these protists. Not only are they large for single cells (some can be seen by the unaided eye), but they contain organelles that parallel in function the organs of multicellular creatures. In fact, some biologists consider the ciliates to be acellular (not cellular) rather than unicellular in order to emphasize that their "body" is far more elaborate in its organization than any cell out of which multicellular organisms are made.
- At least one small, diploid (2n) micronucleus. It contains the entire genome but is not active in gene transcription.
- A large, polyploid macronucleus that contains the active genes that run the cell.
Sexual reproduction in Ciliates
- Two parents come together and two parents separate. What kind of reproduction is that? you may well ask.
But the process they have been through is the very essence of sexual reproduction - genetic recombination. The "offspring" are not the same as the parents. They are new individuals and their macronucleus will soon reflect that fact.Ciliated protozoans have been the source of several important discoveries in biology, for example:
- The first ribozymes were found in Tetrahymena thermophila.
- Telomerase was also discovered in Tetrahymena thermophila.